For most of the historical life of bicycles the frames were made by assembling metal tubes in the familiar configuration comprising: a generally horizontal top tube connected at its front end to a relatively short head tube and at its rear end to the upper end of a seat tube, a down tube connected to the head tube and extending downwardly and rearwardly to a bottom bracket where the seat tube and the down tube are connected, and pairs of tubular seatstays and chainstays extending rearwardly on opposite sides of the rear wheel area from the upper end of the seat tube and from the bottom bracket, respectively, to dropouts which interconnect the stays and support the rear axle of the bicycle. In a custom made frame the lengths of the top tube and the seat tube and the angle of the seat tube with respect to the horizontal are closely dependent on the size of the rider. The angle of the head tube with respect to the horizontal is dependent on the desired steering characteristics. The length and angle of the chainstays depend on both the height of the frame above the ground and the desired riding stiffness and pedaling efficiency. Thus there are many variable dimensions which must be accommodated in making a frame for a particular rider's size and performance needs.
In recent years through the use of reinforcing lugs to aid in interconnecting tubes, and through the use of improved aluminum and steel alloys and titanium for tubes, stronger and lighter weight frames became available. However the strength of these metal materials can be easily exceeded on a strength to weight ratio by composite structures such as carbon, boron, aramid and other synthetic non-metallic fibers bound together with suitable resins. Tubes made from such synthetic fibers have been used in frames to replace the top, down, seat and stay tubes, but there remains a problem in anchoring the ends of the tubes to the other components of the frame with sufficient strength at the joints to accept the high stresses thereat without structural failure.
The strength of a frame and its stiffness properties are dependent on both the strength of the frame where the tubes are interconnected and on the strength of the tubes themselves along their lengths. Two tests for measuring frame strength and stiffness as parameters of well-known frame riding characteristics are described in U.S. Pat. No. 4,500,103 to Klein. These tests are called Bottom Bracket Torsion Test and Lateral Bending Stiffness Test. Klein merely states that the various parts of the frame are attached in a suitable manner so as not to lose strength or rigidity at the joints. His preferred configuration uses welded or brazed joints with subsequent heat treatment where applicable with possible use of lugs which are well known. Klein mention, but does not illustrate nor describe, other joining devices or means. Moreover, although Klein mentions possible use of carbon, boron or other synthetic fibers, he does not disclose any method of making a frame of such materials which meets his selected test parameters.